The Properties of Galactic Globular Clusters at Birth

Nathan Leigh (American Museum of Natural History)

January 08, 2015

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Abstract: Only massive globular clusters (GCs) can survive for a Hubble time in the tidal field of our Galaxy. The rest dissolve, dispersing their stars into the Galactic field. Thus, GCs contain the fossil record of a very early episode of star formation in our Galaxy, and are our only means of studying stellar birthing in the early local Universe. In this talk, we present the results of a suite of Monte Carlo and N-body simulations for globular cluster (GC) evolution. The models are used to constrain the parameter space relevant to the formation of the Milky Way GC population. That is, the set of initial conditions that will evolve dynamically over ~10–12 Gyr to reproduce the presently observed parameters for the bulk of the Galactic GC population. Along with a universal initial stellar mass function, we assume an universal initial binary fraction near unity with a significant soft component, combined with initial densities in the range ^4-10^6 mathrm{M}_{odot} mathrm{pc}^{-3}$ and an initial mass- density relation corresponding to higher densities in initially more massive clusters. These initial conditions are able to simultaneously reproduce the present-day observed structural parameters (concentration, mean density, total cluster mass, etc.), stellar mass functions and binary fractions (both inside and outside the half-mass radius) for most Galactic GCs. Our results provide important constraints for simulations of clustered star formation in the proto-Milky Way.